Allow custodians to run multiple instances of the bot

[Desrever Nu]

Currently it creates some problem (logging folders and runtime resources?)

And remember to edit documentation (setup.md )

**You can only run ONE instance of nubot at the time. To run multiple instances simoultaneusly, you can create one separate nubot folder for each instance. FIX coming soon **

[Benjamin Cordes]

Tested on branch 392 and works. Perhaps we should later implement a policy that if several bots run, they have to run on separate exchanges